This invention relates to aerofoil bodies. It relates in particular to aircraft wings of the kind presenting leading edges that are strongly swept relative to the direction of motion of the craft through the surrounding air. An extreme and relatively familiar version of such a wing is the so-called "delta" wing, the plan shape of which approximates to an isosceles triangle. Other known versions of such a wing have curved leading edges, and the wing tips need not be pointed.
In the accompanying drawings FIG. 1 is a diagrammatic perspective view of such a wing, and FIG. 2 illustrates the spanwise lift distribution of such a wing diagrammatically. In FIG. 1 a "delta" wing 1 presents leading edges 2, 3 and a trailing edge 4. Reference 5 indicates the fore-and-aft centreline of the wing in flight, and arrow 6 the "free stream" direction of the surrounding fluid relative to the wing in use. It is well known that when such a wing is placed at a positive incidence to an airflow it will develop a pattern of flows in which vortex sheets, separating from close to the swept leading edges, will roll up to form two strong coiled vortex sheets approximately conical in form. Such sheets are indicated by references 7 and 8. Secondary vortex sheets, as indicated by references 9 and 10, may also form between the main sheets and the leading edges: however the size of the secondary sheets is very much smaller and consequently their effects are small also. The axes of vortex sheets 7 and 8 are indicated at 11 and 12, and it will be seen that they lie above wing 1 and inboard of leading edges 2 and 3: regions of low pressure are induced against the top surface of the wing underneath these axes. At all but very low incidences the lift distribution across the span of such a wing is as illustrated in FIG. 2 and it is well known that as incidence increases, the peak lift values 13 occurring immediately beneath axes 11, 12 increase more rapidly than the lift value 14 which occurs over wing centreline 5.
However, relative motion between the wing and the surrounding fluid causes vortex sheets to be shed not only above the surface of the wing itself, but also downstream of the trailing edge of the wing. The present invention arises from appreciating that the trailing edge vortex sheet can be modified with good effect. FIG. 3 of the accompanying drawings illustrates such a vortex sheet formation schematically. As a result generally of the spanwise lift distribution illustrated in FIG. 2, and particularly of the fact that maximum lift does not coincide with centreline 5, the sign of the vorticity of the vortex sheet 7 once shed downstream from trailing edge 4 varies across the span of the wing. FIG. 3 illustrates the condition of the part 15 of the sheet just inboard of the line of maximum lift created by the axis 11 of the sheet and it will be seen that the sign of the vortex at this part of the sheet is opposite to the sign of the more forward and outward part 15a. At moderate and greater incidences this difference in sign has the effect of keeping axis 11 of vortex sheet 7 closer to leading edge 7, and thus further from centreline 5, than would be the case if the strength of part 15 of the sheet were less. This is disadvantageous: ideally maximum lift should occur at the centre.